Cross-regulation of Immunometabolism and Circadian Pathways in Obesity Pathophysiology

Project Summary
Obesity and diabetes are increased among individuals subjected to shiftwork, reduced sleep, and social jetlag.
High fat diet (HFD) misaligns intrinsic circadian cycles with the light/dark cycle and alters oscillations of metabolic
genes in visceral adipose tissue, a key site in the control of energy balance, glucose regulation, and inflammatory
disorders. Conversely, restricting HFD to the dark period only realigns meal time with circadian rhythms and
enhances insulin sensitivity, promoting healthful obesity. How circadian disruption in visceral adipose tissue
contributes to obesity pathophysiology remains unknown. In exciting new data, we show strong day/night
rhythms in adipocyte mitochondrial respiration with maximal uncoupling at the onset of the active period that is
dependent upon a functional clock. Further, 13C-glucose entry into the tricarboxylic acid (TCA) cycle is also
highest at the beginning of the active period, indicating autonomous circadian control of WAT metabolic flux
across the day/night cycle. Surprisingly, in Bmal1-/- adipocytes, we observe reprogramming of adipocyte
metabolism with increased 13C labeling in succinate and reduced levels of other TCA intermediates, a signature
of stress and ROS accumulation. Here we seek to test the hypothesis that the circadian clock controls
energy flux within visceral adipose tissue at the level of fuel entry into the TCA cycle through a process
disrupted by HFD. In Aim 1, we will test the hypothesis that circadian coordination of feeding time and adipose
energy utilization cycles promote healthful adipose expansion using genetic lineage tracer animals and metabolic
phenotyping. We will assess adipose tissue remodeling and 13C glucose flux into the TCA cycle in addition to
lipid and organic acids across the light-dark cycle in mice fed regular chow or HFD either ad lib or time-restricted
to the light (misttimed feeding) or dark (optimal time feeding) period at thermoneutrality (30oC). We will also test
the requirement of the WAT clock and the effect of adipose-specific BMAL1 overexpression in HFD on adipose
remodeling, inflammation, fibrosis, and glucose homeostasis. Aim 1 results will establish the interplay
between the WAT clock and feeding time in energy flux, metabolic health, and capacity for healthful
adipose expansion, particularly with the new addition of the light-only feeding group for comparison to the dark-
only and AL cohorts. In Aim 2, we will test the hypothesis that HFD abrogates circadian energetic cycles in
visceral adipose tissue and induces epigenetic remodeling towards a proinflammatory cell fate. We will perform
tandem chromatin and expression profiling in adipocytes to identify the time signature and molecular drivers of
visceral WAT remodeling in ad lib and light- and dark-only-fed mice on HFD. Finally, we will examine whether
BMAL1 overexpression during HFD preserves the healthful chromatin landscape of regular chow fed mice.
Results of Aim 2 will determine how clock control of chromatin activity and transcription contributes to
healthful obesity. Collectively, these studies will define the role of time-of-day in adipogenesis and nutrient flux,
uncovering novel targets to combat the immunometabolic complications of obesity and circadian disruption.

Grant Number: 5R01DK127800-05
NIH Institute/Center: NIH
Principal Investigator: Joseph Bass